The cell surface of animal cells has been implicated to participate in a number of important biological processes unique for multicellular organisms. It is generally assumed that the cell surface, either based on its detailed chemistry, topological rearrangements or by processes including assembly, turnover and dynamic interactions with other organelles, plays a key role in the regulation of cellular proliferation and in cell-cell interaction in normal and malignant cells. The aim of the research project is to elucidate the structure and functions of mammalian cell surface through the isolation and biochemical characterization of somatic cell mutants. More specifically, we plan: a. to isolate and characterize CHO mutants resistant to cytotoxic lectin abrin. b. to isolate and characterize CHO mutants altered in the structural and functional integrity to cytoskeleton-membrane complex by using chemicals believed to interact with surface modulating assemblies, and c. to ascertain the physiological consequences of these mutations. By ascertaining the cause-effect relationship between the alteration in cell surface component and the loss of growth control, we may gain a better insight into the pathogenesis of neoplasia at the cellular and molecular level.